Mealworms are never a great idea when it comes to feeding bearded dragons. The thicker exterior shell of a mealworm prevents the proper absorption of vital nutrients, which a mealworm is also lacking. The other downfall to mealworms is that they can cause impaction in dragons. Impaction or blockage in the intestinal tract or digestive system is most likely one of the most common illnesses in dragons. Thus feeding softer bodied feeders is always the best idea.
With the crickets ensure that they are the right size feeders for your dragon as eating crickets which are too large for them can also cause impaction and or paralysis. I have had my dragons completely ignore crickets sometimes and other times eat them, some times they wont touch crickets unless they are dusted. Typical odd behaviors of our little pets. Variety can help with this, or perhaps tasting mealworms has shun his interest in the not so great tasting crickets.
With the salad, it is not uncommon for a 3 month dragon to completely disregard it's salad. There are some tricks to try though. One, try dropping pieces from a distance so they seem as if they had movement. Movement can spark interest. Which leads to number two, put feeders in with the salad. Number three, the dragon may not know what they are missing, take a small piece and slide it into your dragons mouth (gracefully) starting from a corner and working your way to the front. Once in the front your dragon generally will open it's mouth giving it a taste. I wouldn't try this too much as dragons can catch on to this and purposely not open their mouths or possibly develop a lack of interest to the salad.
At 3 months a dragons main intake (80-90%) will be feeders, if they don't eat their salad at this age don't fret. Once a dragon gets 1.5 years this should change, their diet interests will lean heavily toward salad items and put live feeders down to 10-20% of their diets.
Are you dusting the feeders and or salad? What are you using for a UV source?
